On 09.02.15 14:48, raymond.hettinger wrote:

https://hg.python.org/cpython/rev/dc820b44ce21 changeset: 94572:dc820b44ce21 user: Raymond Hettinger date: Mon Feb 09 06:48:29 2015 -0600 summary: Mirco-optimizations to reduce register spills and reloads observed on CLANG and GCC.

files: Objects/setobject.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/Objects/setobject.c b/Objects/setobject.c --- a/Objects/setobject.c +++ b/Objects/setobject.c @@ -84,8 +84,9 @@ return set_lookkey(so, key, hash); if (cmp > 0) /* likely */ return entry; + mask = so->mask; /* help avoid a register spill */

Could you please explain in more details what this line do? The mask variable is actually constant and so->mask isn't changed in this loop.